It regrows to the exact size it was, no extra skin no less skin. Unless of course it’s a serious injury but I’m talking minor skin removal. Obviously gunshot wounds, flesh eating bacteria and animal bites don’t do this because of scar tissue I assume but even with them it’s remarkable how close it comes to filling in the area. How does the body know when to stop growing the new tissue to fill it in and how come with these deeper wounds the body has a harder time figuring it out?
In: Biology
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The skin on the end of your finger is much thicker than you think it is. Most cuts don’t go all the way through the skin. If it does you will regrow smoother scar tissue. If there are some of the lower skin layers left, the end will grow back complete with fingerprints.
Basically every cell in your body has an internal set of instructions to follow. For skin, one of the primary jobs is to either grow or not. So each skin cell is sitting there and constantly going over a checklist of if it’s time to divide or not. “Ok, has it been a while since the last time I divided? Yup. Am I big enough? Yup. Is there room for another cell next to me? Nope…dang. Start over.” So, if you have a wound your skin cells recognize that there’s not skin cells next to them and start dividing to fill the gap. Once they’re surrounded by skin cells they stop.
A “fun” fact is that this is pretty much what cancer comes from. Basically something (radiation, chemicals, copy error, dumb luck) damages the “check list”. Most of the time when the list is damaged it will be unintelligible and the cell will just sit idle until it dies, but once in awhile the list is damaged in such a way that it most of the conditions that would trigger a stop get ignored. “Ok, has it be awhile since I last divided? Who cares. Am I big enough to divide? Your mom thought I was big enough. Is there room next to me? Fuck it, it’s go time!” So the cell divides like crazy making a bunch of cells that divide like crazy.
edit: welp, thanks for all the replies and metals, but now I’m gonna be late for work. Thanks jerks 😉 ! Also, a couple of people have said I’m wrong which honestly doesn’t surprise me much. Don’t, like, make any serious medical decisions based on some rando on reddit in a sub based on explaining things as if to children, k?
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As an embryo growing from a single cell, different parts of the genome get activated in order to tell certain cells to take on different roles. As they grow to become functional parts, each segment of your finger has slightly different genetic activations which tell it “where” it is in your finger and how it is supposed to act and develop. When part gets cut off and regrows, the gradient of activated or deactivated genetic segments can be recreated and therefore “know” what type of tissue should be created and how much of it (roughly) from the patterns laid down during embryonic development for cell differentiation at the very beginning.
Obviously for larger injuries, the replacement might be too far away for this simple trick to work, but that’s how it does it on the small scale.
You might enjoy [this fun video on evolutionary development](https://youtu.be/ydqReeTV_vk) which focuses on how these changes evolve and were laid down in the first place, but also has some famous examples on how differentiation and “cells knowing what to be” works and how that can go wrong if you mess with it (like flys that grow eyes in their ass or legs on their faces if you inject different proteins into different segments during development).
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